Transition metal chalcogenides have received attention in various applications, including thermoelectrics, magnetic semiconductors, superconductors, quantum dots, sensors, and photovoltaics because of their unique structures and electrical properties. A significant number of high-quality metal chalcogenide nanostructures have been prepared employing colloidal synthetic approach. Most previous studies have focused on Groups 2-4 semiconductor nanostructures, such as CdSe, CdS, Zns, ZnSe, CdTe, CdSe, Ag2Se, NiSe, and Ag2S and have investigated their optical properties.
However, other potential semiconducting metal chalcogenide nanostructures, especially materials having phase-selectivity problems in the synthesis, have not been investigated until now. For example, iron selenides have two stoichiometric phases, FeSe and FeSe2. FeSe forms a tetragonal or hexagonal crystal, whereas FeSe2 forms a crystal in the cubic or rhombic (marcasite-type) structure. Both phases have Fe2+ ions and their phase-selective syntheses are challenging. Such iron selenides have excellent conductive, optical, electrical, and magnetic properties with a direct band gap (1.23 eV) and can be semiconductors or even superconductors with the characteristics of ferromagnetic/ferrimagnetic metals. For example, PbO-type FeSe exists only in a narrow synthesis zone of 50.6 to 51.0%. It is known that iron elements become superconductors when they have very accurate compositional and specific structural features. NiAs-type FeSe is also a very rare 1:1 Fe—Se compound, exists in a synthesis zone of 42.0 to 50.5%, and is not a superconductor. However, only few iron selenides are known so far. Despite many efforts to synthesize PbO-type FeSe nanoparticles, studies on the optical properties of other potential semiconducting iron chalcogenide nanocomposites still remain in the early stages. Furthermore, attempts to synthesize highly photoluminescent iron chalcogenide nanocomposites have not been successful.